Bordetella pertussis, microorganism which causes the disease commonly known as whooping cough, produces several toxins (i.e., pertussis toxin (PT) and heat labile or dermonecrotic toxin) (see project Z01 HD 01306 01) which appear to play important roles in pathogenesis of the organism. PT, in addition, is a major protective antigen which is a promising candidate for the development of a new acellular pertussis vaccine. The current project concentrates on elucidating the mechanisms by which pertussis toxin interacts with cells and elicits its diverse pharmacologic actions. The initial event in the interaction of PT with cells appears to be a rapid and essentially irreversible binding of toxin to cells. Using the interaction of PT with fetuin as a model, studies have been conducted which demonstrate that PT interacts with the carbohydrate moieties pressent in fetuin. The structure of the carbohydrate responsible for interaction with PT has been characterized and binding constants have been determined. The toxic action of PT is mediated by toxin catalyzed transfer of the ADP-ribose moiety from NAD to the adenylate cyclase regulatory component, Ni. This action of PT has been used as a probe to explore the role of Ni in regulation of cell function, and the changes of the regulatory component in response to desensitization. These studies have shown that PT catalyzed modification of Mi reduces receptor affinity and abolishes the action of GTP in producing the high affinity binding state without blocking the capacity of nonhydrolizable GTP analogs to mediate cyclase activation. Use of PT as a probe to examine Ni following glucogen desensitization of MDCK cells showed increased availability of Ni for ADP-ribosylation. This leads to the suggestion that hormone induced desensitization results from increased Ni or mobilization of Ni to pools that affect receptor mediated regulation of adenylate cyclase.